|Publication number||US8173910 B2|
|Application number||US 12/178,973|
|Publication date||May 8, 2012|
|Filing date||Jul 24, 2008|
|Priority date||Jul 24, 2008|
|Also published as||CN101636038A, CN101636038B, DE102009027309A1, US20100018763|
|Publication number||12178973, 178973, US 8173910 B2, US 8173910B2, US-B2-8173910, US8173910 B2, US8173910B2|
|Inventors||Alan L. Barry|
|Original Assignee||GM Global Technology Operations LLC|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Classifications (13), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention generally relates to printed circuit board (PCB) surface mount systems and, more particularly, to a high density PCB ball grid array system having an improved mechanical strength that is well-suited for use within high vibration environments.
Ball grid arrays (BGA) are a relatively new type of surface mount packaging wherein a matrix of solder balls is utilized to provide mechanical and electrical coupling between at least one electronic component and a host printed circuit board (PCB). A representative BGA-to-PCB interface may be formed by first depositing solder paste on selected BGA pads in a grid of BGA pads formed on a mounting surface of a host PCB. An electronic component, which has a corresponding grid of BGA pads formed thereon, is then positioned over the PCB. The electronic component is positioned such that each solder ball resides between and contacts a BGA pad of the electronic component and a BGA pad of the PCB. A reflow process is subsequently performed wherein the assembly is heated (e.g., via an infrared heater) while the electronic component is urged toward the PCB in a controlled manner (e.g., by a robot). As it approaches its melting point, each solder ball deforms and adheres to the bonding surfaces provided on the PCB pads. Each solder ball in the BGA thus forms a mechanical and electrical connection between the host PCB and the electronic component.
The continual demand to decrease the size and weight of electronic components has lead to the development of high density BGAs (also commonly referred to as “fine pitch BGAs”). In such high density BGAs, the outer diameter of each BGA pad provided on the PCB is reduced. This reduction in the size of the PCB BGA pads permits spacing between the pads and other conductive elements (e.g., plated through-hole vias) located on the PCB to be decreased; however, this reduction in the size of the PCB BGA pads also results in a corresponding decrease in the bonding surface area of each BGA pad and, therefore, a decrease in the overall mechanical strength of the BGA-to-PCB interface. In many applications, this decrease in mechanical strength is acceptable and does not negatively impact the reliability of the BGA-to-PCB interface. However, this decrease in mechanical strength may render the BGA-to-PCB interface unsatisfactory for use in certain applications wherein significant mechanical stressors (e.g., high vibratory forces) are routinely experienced, such as deployment within the inverter assembly of an electric or hybrid vehicle.
At least two main approaches have been introduced to increase the mechanical strength of the BGA-to-PCB interface in high density BGAs. In a first approach, the volume between solder balls and under the BGA is filled with an adhesive, such as epoxy glue. The epoxy glue significantly increases the strength of the BGA-to-PCB interface by bonding each solder ball to surrounding components of the PCB (e.g., the PCB BGA pad, the soldermask, etc.). However, the underfilling of the epoxy also adds undesirable cost and complexity to the manufacturing procedure. Furthermore, cracks or fractures may develop during device operation due to a difference in the coefficient of thermal expansion between the epoxy and the BGA package.
The strength of the BGA-to-PCB interface may also be increased by moving the plated through-hole vias into some or all of the PCB BGA pads and such that the vias are no longer located between the BGA pads on the circuit board. Such a via-in-pad approach permits the outer diameter, and thus the area of the bonding surface, of each BGA pad to be increased thereby improving the overall mechanical strength of the BGA-to-PCB interface. However, such a via-in-pad approach also increases the likelihood that solder may weep into the via through-hole during device processing. Although the via through-holes may be plugged with epoxy to prevent such solder weeping, the process of plugging the via through-holes adds considerable cost and complexity to the manufacturing process.
It should thus be appreciated that it would be desirable to provide a high density PCB BGA system that achieves a relatively high mechanical strength. Preferably, embodiments of such a PCB BGA system would be reliable and relatively inexpensive to produce. It would also be desirable for embodiments of such a PCB BGA system to provide an efficient heat dissipation path through the BGA-to-PCB interface. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
A printed circuit board (PCB) ball grid array (BGA) system is provided. In one embodiment, the PCB BGA system includes a PCB, a PCB BGA pad formed on the PCB, a plated through-hole via disposed at least partially through the PCB proximate the PCB BGA pad, and a soldermask disposed over the PCB. The soldermask includes: (i) a BGA pad opening through which the PCB BGA pad is exposed, and (ii) a via opening through which a central portion of the plated through-hole via is exposed. The via opening has an inner diameter that is less than the outer diameter of the plated through-hole via.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.
As shown in
An insulative soldermask 36 (e.g., a liquid photoimageable soldermask) is formed over PCB substrate 26. The illustrated portion of soldermask 36 includes two openings therethrough, namely, a BGA pad opening 38 and a via opening 40. BGA pad opening 38 exposes BGA pad 28 through soldermask 36 to permit the soldering of pad 28 as described more fully below. Similarly, via opening 40 exposes plated through-hole via 30 through soldermask 36. This substantially prevents material from soldermask 36 from flowing into longitudinal channel 34 during device processing.
As noted above, a surface-mountable electronic component 22 is mounted on PCB BGA system 20. Electronic component 22 includes, among other non-illustrated elements, a BGA substrate 42 having a BGA pad 44 formed thereon. For clarity, BGA pad 44 may be referred to herein as “the component BGA pad,” while BGA pad 28 may be referred to herein as “the PCB BGA pad.” Notably, PCB BGA pad 28 has a smaller outer diameter than does component BGA pad 44. A solder ball 46 resides between component BGA pad 44 and PCB BGA pad 28. Solder ball 46 is illustrated in
As indicated in
Referring collectively to
To permit the dimensions of PCB BGA system 20 to be minimized, the outer diameter of PCB BGA pad 28 may be reduced; e.g., as stated above, pad 28 may have an outer diameter of approximately 0.50 mm. While permitting the envelope of PCB BGA system 20 to be minimized, this reduction in the size of PCB BGA pad 28 also decreases the mechanical strength of the soldering joint formed between PCB BGA pad 28 and component BGA pad 44 and, therefore, the overall mechanical strength of the PCB-to-BGA interface. As a result, PCB BGA system 20 may not be suitable for use in applications characterized by significant mechanical stressors, such as high vibratory forces. To address this issue, an exemplary PCB BGA system will now be described in conjunction with
An insulative soldermask 76 is formed over the illustrated layer of PCB substrate 64. As a non-limiting example, soldermask 76 may comprise an insulative film (e.g., a liquid photoimageable or dry film) onto the upper surface of PCB substrate 64. The illustrated portion of soldermask 76 is formed to include two openings therethrough; i.e., a BGA pad opening 78 through which PCB BGA pad 66 is entirely exposed, and a via opening 80 through which plated through-hole via 68 is partially exposed. It should be noted at this juncture, and as will be discussed in more detail below, via opening 80 is formed such soldermask 76 encroaches over, but does not fully cover, the upper surface of plated through-hole via 68.
PCB BGA system 60 further includes a solder ball 82, which is shown in
As shown most clearly in
Referring still to the exemplary embodiment shown in
Separating portion 90 of soldermask 76 is preferably formed to have a sufficient width to act as a dam to prevent solder from flowing onto neighboring pads. As may be appreciated by comparing
In addition to increasing the area of the BGA pad bonding surface, PCB BGA system 60 enhances the mechanical strength of the BGA-to-PCB interface in another manner; i.e., by causing solder ball 82 to flow into the circumferential clearance provided around PCB BGA pad 66 and circumferentially adhere to BGA pad 66. This is accomplished by increasing the width of circumferential clearance 95 (labeled in
It should thus be appreciated that there has been provided an exemplary embodiment of a high density PCB BGA system having an improved mechanical strength. Embodiments of the above-described PCB BGA system are relatively durable, inexpensive to manufacture, and provide an efficient heat dissipation path through the BGA-to-PCB interface. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5591941 *||Oct 28, 1993||Jan 7, 1997||International Business Machines Corporation||Solder ball interconnected assembly|
|US6512185 *||Mar 14, 2001||Jan 28, 2003||Sony Corporation||Printed-wiring board|
|US6543128 *||Apr 11, 2002||Apr 8, 2003||Siliconware Precision Industries Co., Ltd.||Ball grid array package and its fabricating process|
|US20050230147 *||Jun 13, 2005||Oct 20, 2005||Nec Corporation||Wiring board, and electronic device with an electronic part mounted on a wiring board, as well as method of mounting an electronic part on a wiring board|
|US20070062730 *||Jan 9, 2006||Mar 22, 2007||Litton Systems, Inc.||Controlled depth etched vias|
|US20090032294 *||May 16, 2008||Feb 5, 2009||Phoenix Precision Technology Corporation||Circuit board|
|U.S. Classification||174/263, 361/761|
|International Classification||H05K1/18, H05K1/11|
|Cooperative Classification||H05K3/3436, H01L2224/16225, H05K2201/0949, H05K3/3452, H05K2201/099, H05K1/116, H05K3/42, H05K1/111|
|Jul 24, 2008||AS||Assignment|
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS, INC., MICHIGAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BARRY, ALAN L.;REEL/FRAME:021286/0578
Effective date: 20080716
|Nov 8, 2010||AS||Assignment|
Owner name: WILMINGTON TRUST COMPANY, DELAWARE
Free format text: SECURITY AGREEMENT;ASSIGNOR:GM GLOBAL TECHNOLOGY OPERATIONS, INC.;REEL/FRAME:025324/0475
Effective date: 20101027
|Feb 10, 2011||AS||Assignment|
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS LLC, MICHIGAN
Free format text: CHANGE OF NAME;ASSIGNOR:GM GLOBAL TECHNOLOGY OPERATIONS, INC.;REEL/FRAME:025781/0211
Effective date: 20101202
|Nov 7, 2014||AS||Assignment|
Owner name: GM GLOBAL TECHNOLOGY OPERATIONS LLC, MICHIGAN
Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:WILMINGTON TRUST COMPANY;REEL/FRAME:034384/0758
Effective date: 20141017